Fluorination catalyst and process

ABSTRACT

A chromia-based fluorination catalyst in which the chromia is at least partially crystalline and which may contain a zinc or a compound thereof, the production of the catalyst by sintering amorphous chromia and its use in fluorination processes.

[0001] This invention relates to a fluorination catalyst and theproduction and use thereof and particularly to an improved fluorinationcatalyst based on chromia, a process for producing the catalyst and afluorination process using the catalyst.

[0002] Fluorination processes comprising reaction of a starting materialwith hydrogen fluoride to introduce one or more fluorine atoms into thestarting material are well known and are used extensively in industry.Vapour phase processes in which the starting material and hydrogenfluoride are reacted in the vapour phase at elevated temperature arecommon and such processes usually employ a fluorination catalyst whichoften is a catalyst comprising or based on chromia which has beensubjected to a pretreatment with hydrogen fluoride to provide theworking catalyst. It is generally accepted that chromium oxide catalystsof high surface area and wherein the chromium is present as chromium(III) have high initial activity and that such active chromia catalystsare in an amorphous or essentially amorphous state. A recent developmentin chromia catalysts is a catalyst of enhanced activity produced byincorporating an activity-promoting amount of a divalent metal oxidesuch as an oxide of zinc, nickel or cobalt, especially zinc, in thecatalyst, the oxide or at least the chromia remaining in the essentiallyamorphous state and having a large surface area. Catalysts containingother divalent metal oxides such as magnesia have also been proposed.

[0003] When used in the production of hydrofluorocarbons [HFCs], theknown chromia catalysts and especially those promoted by a divalentmetal such as zinc have a high initial activity and can result in highconversions and high selectivities. They suffer from a progressivereduction in activity due to deposition of coke on the catalyst but theycan be regenerated a number of times by heating in an oxygen-containingatmosphere such as air or a mixture of air with hydrogen fluoride andhave a reasonable and generally acceptable lifetime. However, thecatalysts suffer the disadvantage that they are not particularly robust,especially in respect of chemical robustness and are deteriorated underthe conditions of use and especially when subjected to high temperaturesin the presence of hydrogen fluoride so that their lifetime leavessomething to be desired.

[0004] The present invention is based on the discovery that therobustness of chromia-based catalysts and hence their useful workinglifetimes is increased by inducing or introducing crystallinity andpreferably a controlled degree of crystallinity into the chromia.Moreover, the initial activity of the catalysts can be slightly butsignificantly enhanced, without a reduction in selectivity, byintroducing an activity-promoting amount of zinc or a compound of zincinto the catalyst.

[0005] According to the first aspect of the invention there is providedan improved chromia-based fluorination catalyst wherein the chromia isat least partially crystalline.

[0006] Preferably, the chromia exhibits an apparent degree ofcrystallinity as represented by alpha chromia type crystals greater than8%, preferably greater than 20%, and less than 50% by weight.

[0007] Introducing crystallinity into the chromia results in a decreasein the surface area of the catalyst and too high a degree ofcrystallinity results in an unacceptably low surface area, for examplebelow 20 m²/gm. The degree of crystallinity in the catalyst can becontrolled so as to result in a catalyst having a surface area greaterthan about 20 m²/gm, preferably from about 30 to about 70 m²/gm.

[0008] According to a further aspect of the invention, there is providedan improved zinc-promoted chromia fluorination catalyst wherein thechromia is at least partially crystalline and the catalyst compriseszinc or a compound of zinc in an amount of less than about 3% by weightof the catalyst.

[0009] In a further aspect of the invention there is provided animproved zinc-promoted chromia-based fluorination catalyst wherein thechromia is at least partially crystalline produced by inducingcrystallinity in chromia and subsequently introducing zinc or a compoundof zinc into the crystallised chromia by impregnation with a solution ofa soluble zinc salt. The catalyst preferably contains from 0.1% to about2% by weight of zinc or a compound of zinc depending upon the degree ofcrystallinity induced in the chromia.

[0010] Inducing crystallinity in the chromia results in a decrease inthe surface area of the catalyst and a very high a degree ofcrystallinity results in a very low surface area, for example below 10m²/gm. The degree of crystallinity in the catalyst of the invention canbe controlled such that the catalyst has a surface area greater thanabout 20 m²/gm, preferably from about 30 to about 70 m²/gm.

[0011] Suitably, the catalyst according to the first aspect of theinvention contains zinc or a compound of zinc. A catalyst according tothe invention may contain an activity-promoting amount of a divalentmetal such as cobalt, magnesium or nickel or a compound thereof inaddition to or instead of zinc or a zinc compound. Nevertheless, thepreferred metal is zinc and in this case the amount of the zinc isimportant since it is known that zinc can act as a catalyst poison ifpresent in too large an amount. We have found that whilst theactivity-promoting amount of zinc in catalysts wherein the chromia isamorphous is generally greater than about 2% by weight and usuallygreater than about 5% by weight depending upon the method of productionof the catalyst, the activity promoting amount of zinc in the partiallycrystallised catalysts of the invention should generally be less thanabout 2% by weight, preferably no greater than about 1% by weight.

[0012] According to a preferred embodiment of the invention there isprovided a chromium-based fluorination catalyst comprising from 0.1 to2% by weight of zinc or a compound of zinc wherein the chromia is atleast partially crystalline. The catalyst preferably has an apparentdegree of crystallinity as represented by alpha chromia type crystals offrom about 8% to about 50% and has a surface area greater than about 20m²/gm.

[0013] If present, the amount of divalent metal other than zinc in thecatalyst, whether the divalent metal be an activity promotor or not, isnot critical since such metals are not generally regarded as catalystpoisons even if present in large amounts. The amount of such metals mayvary over a wide range up to 50% by weight or even higher of thecatalyst, although the amount will usually be in the range from about 5%to about 25% by weight.

[0014] The apparent degree of crystallinity or the degree ofcrystallinity induced in the chromia is determined by X-ray diffractionanalysis using the standard NIST [National Institute of Standards andTechnology] technique and comparing the result with that obtained byanalysis of a pure alpha chromia standard prepared by sintering chromiaat 1223 K in air for 24 hours (100% crystallinity). The catalysts do nothave a true alpha chromia structure so that the % degree ofcrystallinity determined by comparison with the results for pure alphachromia is not a true % degree of crystallinity and therefor is referredto herein as the “apparent degree of crystallinity”. Morover, since thecatalyst structure is not true alpha chromia so that the X-raydiffraction peak tends to be slightly distorted, the apparent degree ofcrystallinity is expressed herein as being represented by “alpha chromiatype crystals”.

[0015] The apparent degree of crystallinity as represented by alphachromia type crystals is determined by measuring the integrated area ofthe 104 peak of both the catalyst sample and the pure alpha chromiastandard (at ca. 33.6 ° 20 for Cu K radiation) between 32.5 and 35.0 °20, subtracting the background to provide corrected integrated areas andthen ratioing the corrected area for the catalyst sample to thecorrected area for the standard sample.

[0016] The catalyst exhibits an X-ray diffraction peak at a spacing oflattice planes from 2.65 to 2.7 of half maximum peak width less than 0.8degrees.

[0017] Preferably the chromium in the catalyst is present as chromium(III) although a small amount, say up to 10%, of chromium (VI) may bepresent as a result of the conditions under which the chromia iscrystallised. As described hereinafter, crystallinity can be induced inthe chromia by sintering the catalyst at elevated temperature and thismay be carried out under an inert atmosphere or in the presence of air.Catalysts produced by sintering in an inert atmosphere tend to compriseessentially chromium (III) but require higher sintering temperatureswhilst those produced by sintering in air tend to contain some chromium(VI) but require lower sintering temperatures. We prefer to sinter thecatalysts under an atmosphere of air or a mixture of air and nitrogensince these conditions enable relatively low temperatures of 300° C. to450° C. to be employed.

[0018] The catalyst of the invention has excellent activity andselectivity and has improved chemical robustness leading to a longworking lifetime. However, the catalyst lacks the physical robustness ortoughness associated with amorphous chromia catalysts and is difficultto handle in practice, for example it is not readily produced in theform of pellets in which fluorination catalysts are usually produced andit does not easily withstand temperature shocks as are often encounteredin the operation of large-scale industrial plants. This problem can bealleviated by blending the improved partially crystalline catalyst witha non-crystalline chromia so that the catalyst may comprise essentiallyamorphous chromia as well as crystalline chromia. Such blended catalystshave improved toughness and can be pelleted and handled without too muchdifficulty. The amount of the non-crystalline (essentially amorphous)chromia additive may vary within wide limits but will usually be fromabout 10% to 60% by weight of the blended catalyst. The non-crystalline(essentially amorphous) chromia may itself contain a divalent metal, forexample an activity promoting amount of a divalent metal such as zinc,cobalt or nickel.

[0019] The partially crystalline catalyst can be produced by sinteringthe corresponding amorphous or essentially non-crystalline catalyst orchromium hydroxide precursor thereof at elevated temperature underconditions whereby the apparent degree of crystallinity induced in thechromia is controlled, for example to between 8% and 50% by weight andsuch a process is provided according to another feature of theinvention.

[0020] Such a process in which the crystallised chromia is subsequentlyimpregnated with zinc or a compound of zinc is also provides a furtheraspect of the invention.

[0021] Sintering may be carried out under an inert atmosphere such asnitrogen gas or in an oxidising atmosphere such as air which mayoptionally be diluted with an inert gas such as nitrogen. Thetemperature of sintering may be within the range from about 400° to 800°C., preferably from 500° C. to 600° C. in an inert atmosphere and fromabout 300° C. to 800° C., preferably from 330° C. to 500° C. in air.Catalysts produced by sintering in nitrogen contain the chromium asessentially only chromium (III) whilst those produced by sintering inair tend to contain some chromium (VI) as well as chromium (III). Asdescribed hereinbefore, we prefer to sinter the catalyst or precursorthereof in a mixed atmosphere of air and an inert gas such as nitrogen.

[0022] The crystallisation of chromia is an exothermic reaction and maybe accompanied by a rapid rise in temperature leading to hot spots orrun-away reaction unless the reaction is controlled. For this reason itis desirable to raise the temperature of the chromia to the desiredsintering temperature and induce crystallisation of the chromia over aperiod of several hours, for example from 1 to 50 hours and preferably 4to 12 hours. We have found that operating in this way enables us tocontrol the reaction and the degree of crystallisation induced in thechromia.

[0023] During sintering and crystallisation, the surface area of thechromia/catalyst is reduced generally from above 100 m²/gm to below 100m²/gm, for example from 150 m²/gm to below 70 m²/gm. We have found thatwithin the range of crystallinity 8% to 50%, the surface area of thecatalyst decreases with increasing crystallinity from about 70 m²/gm toabout 20 m²/gm. The surface area of the catalyst at any particular stageof the sintering procedure gives a guide as to the degree ofcrystallinity in the chromia and provides an indication of sufficientsintering. The degree of crystallinity in the catalyst can be controlledby controlling the sintering conditions.

[0024] The preferred catalysts containing a divalent metal promotor suchas zinc, cobalt or nickel or compounds thereof can be produced byinducing crystallisation in a chromia catalyst already containing thedivalent metal promotor or by creating the partially crystalline chromiabase catalyst and subsequently impregnating it with the divalent metalpromotor. Any of the known techniques for producing chromia-basedcatalysts can be used to produce the precursor catalyst in whichcrystallinity is induced.

[0025] If present, the amount of the divalent metal promotor is known inthe art but as discussed hereinbefore in the case of zinc or a zinccompound the amount generally should be less than is used in amorphouschromia catalysts. Further, the optimum amount of zinc promotor toafford an increased initial catalyst activity depends upon the catalystpreparation method and generally is lower for catalysts made byimpregnation of a pre-crystallised chromia base than for catalysts madeby a route involving coprecipitation of chromium and zinc salts, forexample hydroxides. As a guide, the optimum amount of zinc in a catalystmade by impregnation of a crystalline chromia may be about 0.5% byweight whilst for a catalyst made by the coprecipitation route theoptimum amount of zinc may be about 1% by weight.

[0026] The partially crystalline chromia catalysts of the invention maybe blended with conventional amorphous chromia catalysts in order toimpart physical robustness or toughness to the catalyst and enable it tobe pelleted and handled without serious damage. As describedhereinbefore, the amount of the conventional catalyst additive may befrom about 10% to about 60% or even more of the blended catalyst.

[0027] The improved catalyst of the invention may be used in any of thefluorinaton reactions in which chromia-based catalysts are normallyemployed. These will usually be reactions of halogenated andparticularly chlorine-containing hydrocarbons with hydrogen fluoride inthe gas phase at elevated temperature. Numerous such reactions areoperated commercially and amongst them may be mentioned the fluorinationof halogenated aliphatic hydrocarbons containing from 1 to 6 carbonatoms, for example methylene chloride (to produce difluoro- methane, HFC32); trichloroethylene (to produce 1,1,1,2-trifluoro-2,2-dichloroethane,HCFC 133a and 1,1,1,2-tetrafluoroethane, HFC 134a); HCFC 133a (toproduce HFC 134a); perchloroethylene (to produce pentafluoroethane, HFC125; chlorotetrafluoroethane, HCFC 124; and dichlorotrifluoroethane,HCFC 123); 1,1,2,2-tetrachloroethane (to produce HFC 134) anddichlorotrifluoroethane (to produce HFC 125). The catalyst is alsouseful in the removal of the impurity chlorodifluoro-ethylene (HCFC1122) from HFC 134a by reacting the impurity with hydrogen fluoride toproduce HCFC 133a. Processes employing the above starting materials areused commercially and thus are important but it is to be understood thatthe fluorination process according to the present invention is notlimited to use of these starting materials.

[0028] Included within the invention is a process for fluorinatinghalogenated hydrocarbons which comprises reacting the halogenatedhydrocarbon with hydrogen fluoride in the vapour phase at elevatedtemperature in the presence of the improved fluorination catalystdescribed herein. The conditions such as temperature, pressure, ratiosof reactants and number of reaction steps for carrying out fluorinationreactions using chromia-based catalysts are well known in the art andare generally applicable to the improved catalyst of the invention,although the increased activity of the improved catalyst generallyenables lower temperatures or shorter contact times to be employed thanhave typically been used hithereto.

[0029] When employed in the production of hydrofluorocarbons [HFCs], theimproved catalysts can suffer deactivation due to coke/carbon depositionand may require periodic regeneration. The catalysts can be regeneratedas necessary by conventional regeneration techniques such as heating inair or in a mixed atmosphere of air and hydrogen fluoride and/or aninert gas. The improved catalysts afford the advantage that they requirereplacement less frequently than conventional chromia-based catalystsand have a longer active working lifetime.

[0030] The invention is illustrated but in no way limited by thefollowing examples.

EXAMPLE 1

[0031] An amorphous chromia catalyst containing 1% by weight of zinc wasprepared by the mixed metal hydroxide precipitation technique. 4 litersof 1 molar chromium nitrate [Cr(NO₃)₃] solution were added to 12 ml of 4molar zinc nitrate [Zn(NO₃)₂] solution to form a mixed metal nitratesolution.

[0032] 740 ml of 0.88 molar ammonia solution was prepared and stirredusing an impeller and sufficient of the mixed metal nitrate solution wasadded to it to lower the pH to 7.3 at a temperature of 21° C. Theresulting mixed metal hydroxide precipitate was collected using a flatbed filter and washed with demineralised water. The washed precipitatewas dried in a nitrogen atmosphere for 12 hours at 150° C. and thencalcined under nitrogen gas at 280° C. for a further 8 hours. Theresulting solid was powdered, mixed with 2% by weight of graphite andformed into pellets of density 2 gm/cm³. The catalyst at this stage wasfound to be essentially amorphous (non-crystalline) and had a surfacearea of 239 m²/gm determined by the BET nitrogen absorption method.

[0033] The catalyst pellets were crushed and seived to generate granulesof particle size 0.5-1.5 mm and 4 g of the granules was charged to a 9mm internal diameter reaction tube for sintering. The catalyst washeated at 425° C. for 16 hours in a flow of 18 ml/min of nitrogen mixedwith 1 ml/min of air after which time the air flow was stopped and thecatalyst was cooled to room temperature in the nitrogen flow. Thecatalyst was then discharged from the reactor and was found to have anapparent crystallinity of about 45% with a surface area of 57 m²/gmmeasured by the BET nitrogen absorption method.

[0034] 2 gm of the partially crystalline catalyst was re-charged to thereactor for conditioning and activity testing. The catalyst was dried at300° C. for 30 minutes in a nitrogen flow of 50 ml/min and then washeated at 300° C. in a hydrogen fluoride flow of 20 ml/min untilhydrogen fluoride was detected in the reactor vent stream. The reactortemperature was increased to 380° C. for 16 hours whilst continuing theflow of hydrogen fluoride, prior to measurement of the activity of thecatalyst.

[0035] The catalyst was cooled to 350° C., still in the flow of hydrogenfluoride, and then 5 ml/min of chloro-2,2,2-trifluoroethane [HCFC 133a]was added to the hydrogen fluoride flow to generate a feed having anHF:HCFC 133a molar ratio of 4:1. After 2 hours, the catalyst temperaturewas reduced to 300° C. and the yield of 1,1,1,2-tetrafluoroethane [HFC134a] at 300° C. was quantified by gas chromatographic analysis. Theyield of HFC 134a at 300° C. was 17.2%

COMPARATIVE EXAMPLE A

[0036] For purposes of comparison, the activity of the unsinteredcatalyst was determined. 2 gm of the amorphous catalyst granules wascharged into the reactor and the catalyst was dried, conditioned andtested by the procedure described above except that the sintering stepat 425° C. was omitted so that the catalyst remained essentiallynon-crystalline. The yield of HFC 134a at 300° C. was 7.6%.

COMPARATIVE EXAMPLE B

[0037] For purposes of comparison also, an amorphous chromia catalystcontaining 3% by weight of zinc was prepared as described in Example 1using 36 ml of the zinc nitrate solution instead of 12 ml. The resultingcatalyst had a surface area of 183 m²/gm. The catalyst was granulatedand sieved as in Example 1 and 4 gm of catalyst granules was charged tothe reactor for sintering. The catalyst was heated at 400° C. for 16hours in a flow of 5 ml/min of air after which time the catalyst wascooled to room temperature in a nitrogen flow of 18 ml/min. The catalystwas discharged from the reactor and was found to have an apparentcrystallinity of about 90% with a surface area of 23 m²/gm. Theamorphous and crystalline catalysts were tested as described above.Using the amorphous catalyst, the yield of HFC 134a at 300° C. was 8.6%and using the crystalline catalyst, the yield of HFC 134a at 300° C. wasonly 1.8%.

EXAMPLE 2

[0038] An amorphous chromia catalyst was prepared by the precipitationtechnique. Aqueous ammonia solution was added to an aqueous solutioncontaining chromium to produce a precipitate of chromium hydroxide. Theprecipitate was washed with demineralised water, dried in a nitrogenatmosphere at 150° C. and then calcined under nitrogen at 280° C. for 8hours. The resulting solid was powdered, mixed with 2% by weight ofgraphite and formed into pellets. The chromia was found to beessentially amorphous (non-crystalline) and had a surface area of 176m²/gm determined by the BET nitrogen adsorption method.

[0039] The amorphous catalyst pellets were crushed and seived togenerate granules of particle size 0.5-1.4 mm and 50 gm of the granuleswas charged to a reaction tube for sintering. The catalyst was heated at190° C. in a flow of 20 ml/min nitrogen gas for 2 hours and then thetemperature was raised to 550° C. at the rate of 20° C./hour andmaintained at 550° C. for 24 hours. The catalyst was then cooled to roomtemperature in the nitrogen flow and discharged from the reactor. Thisbase catalyst was found to have an apparent degree of crystallinity ofabout 80% with a surface area of 47 m²/gm.

[0040] 4.95 gm of the base catalyst was added to 0.96 ml of aqueous zincchloride solution (prepared by dissolving 13.54 gm of zinc chloride indemineralised water to provide 250 ml of solution) and the mixture wasstirred and evaporated to dryness to give an impregnated chromiacatalyst containing 0.5% by weight of zinc.

[0041] 2 gm of the impregnated catalyst was charged to an Inconelreaction tube for conditioning and activity testing. The catalyst wasdried at 250° C. for 90 minutes in a 50 ml/min flow of nitrogen gas andwas then heated at 300° C. in a 20 ml/min flow of hydrogen fluorideuntil hydrogen fluoride was detected in the reactor vent streamwhereupon the temperature was raised to 380° C. for 16 hours whilst theflow of hydrogen fluoride was maintained.

[0042] After conditioning as above, the catalyst was cooled to 350° C.,still in the hydrogen fluoride flow and then 5.8 ml/min of1-chloro-2,2,2-trifluoroethane [HCFC 133a] was added to the hydrogenfluoride flow to provide a feed having an HF:HCFC 133a molar ratio of3.4:1. After two hours the catalyst temperature was reduced to about orbelow 300° C. The yield of 1,2,2,2-tetrafluoroethane [HFC 134a] at 297°C. and 288° C. was measured by gas chromatographic analysis. The yieldof HFC 134a at 297° C. was 17.4% and the yield at 288° C. was 14.1%.

EXAMPLE 3

[0043] Using the impregnation procedure described in Example 2, animpregnated chromia catalyst containing 1% by weight of zinc wasprepared from 4.90 gm of base catalyst and 1.92 ml of zinc chloridesolution. 2 gm of the catalyst was conditioned and tested as describedin Example 2 with a yield of HFC 134a at 297° C. of 14% and a yield ofHFC 134a at 288° C. of 11.5%.

EXAMPLE 4

[0044] Using the impregnation procedure described in Example 2, animpregnated chromia catalyst containing 3% by weight of zinc wasproduced from 4.69 gm of base catalyst and 5.77 ml of zinc chloridesolution. 2 gm of the catalyst was conditioned and tested as describedin Example 2 with a yield of HFC 134a at 303° C. of 7.4% and a yield at292° C. of 6.1%.

COMPARATIVE EXAMPLE C

[0045] For purposes of comparison the activity of the base chromiacatalyst (not impregnated with zinc) was determined using theconditioning and testing procedure described in Example 2. The yield ofHFC 134a at 301° C. was 15% and at 283° C. was 6.4%.

1. An improved chromia-based fluorination catalyst wherein the chromiais at least partially crystalline.
 2. A catalyst according to claim 1wherein the chromia exhibits an apparent degree of crystallinity asrepresented by alpha chromia type crystals of greater than 8%.
 3. Acatalyst as claimed in claim 1 or claim 2 in which the chromia exhibitsan apparent degree of crystallinity of greater than 20% by weight.
 4. Acatalyst as claimed in any preceding claim in which the chromia exhibitsan apparent degree of crystallinity of less than 50% by weight.
 5. Acatalyst as claimed in any preceding claim which comprises zinc or acompound of zinc in an amount of less than about 3% by weight of thecatalyst.
 6. A catalyst as claimed in claim 5 in which the zinc orcompound of zinc is present in an amount of 0.1 to 2% by weight of thecatalyst
 7. A catalyst as claimed in any preceding claim which compriseszinc or a compound of zinc wherein the catalyst is produced by inducingcrystallinity in chromia and subsequently introducing zinc or a compoundof zinc into the crystallised chromia by impregnation with a solution ofa soluble zinc salt.
 8. A catalyst according to any preceding claim inwhich the degree of crystallinity in the chromia is controlled so as toresult in a catalyst having a surface area greater than about 20 m²/gm.9. A chromium-based fluorination catalyst comprising from 0.1 to 2% byweight of zinc or a compound of zinc wherein the chromia is at leastpartially crystalline and exhibits an apparent degree of crystallinityas represented by alpha chromia type crystals of greater than 8% andless than 50% by weight and wherein the catalyst has a surface areagreater than about 20 m²/gm.
 10. A chromium based fluorination catalystcomprising a blend of a catalyst as claimed in any preceding claim witha non-crystalline chromia catalyst.
 11. A catalyst as claimed in claim10 in which the amount of the non-crystalline chromia catalyst is fromabout 10% to 60% by weight of the blended catalyst.
 12. A catalyst asclaimed in claim 10 or claim 11 in which the non-crystalline chromiacatalyst itself contains an activity-promoting amount of a divalentmetal selected from zinc, cobalt, nickel and magnesium.
 13. A processfor producing a catalyst as claimed in any one of claims 1 to 9 whichincludes the step of sintering an essentially non-crystalline chromiacatalyst or precursor thereof at elevated temperature
 14. A process asclaimed in claim 13 in which the step of sintering the catalyst isperformed under conditions whereby the apparent degree of crystallinityinduced in the chromia is controlled to between 8% and 50% by weight.15. A process as claimed in claim 13 or claim 14 in which crystallinityis induced in the chromia and subsequently introducing zinc or acompound of zinc into the crystallised chromia by impregnation with asolution of a soluble zinc salt.
 16. A process for producing afluorinated hydrocarbon which comprises reacting a halogenatedhydrocarbon with hydrogen fluoride in the vapour phase at elevatedtemperature in the presence of a catalyst as claimed in claim 1 .
 17. Aprocess as claimed in claim 16 for producing 1,1,1,2-tetrafluoroethaneby reacting 1,1,1-trifluoro-2-chloroethane with hydrogen fluoride.